At the time of the talvisota Winter War, Finland was experiencing the coldest winter of several decades, possibly of the XX Century, with nighttime temperatures certainly droping to -40°...and the Soviet troops had arrived wearing their summer uniforms, having been told that their fraternal Socialist trade unionist brothers in the cities would be welcoming them with open arms and providing shelter. The lucky ones had greatcoats, and they were indeed welcomed with arms; but few made it to the cities, and more died of exposure than from artillery and small arms fire. Nikita Kruschev, who was a company-level Commisar during the Finnish invasion, put the Soviet casualty numbers at a million soldiers; worse, seeing the drubbing handed out by Finlands reservists and amateurs gave Hitler the confidence that his professional Wehrmacht could finish the job in a year or two, and his Army high command agreed. Stalin's purges of the Soviet officer corps certainly helped, and the ineffectual Russian medical support meant that those who were wounded would freeze to death before treatment was even started, not real helpful so far as troop morale went.
At the time of the year [late Nov 1939- March 1940] and that far North on the Arctic Circle, there was only about 4 hours of daylight between darkness, making the feats of Häyhä's rifle marksmanship even more impressive. Helpfully, the only way the Soviets had to keep alive was to build fires, whick nicely backlighted them for a good marksman, whether with a rifle or *Tikkakoski mowing machine*.
And, of course, Häyhä has an olympic-level targetwshooter and hunter. Once he developed procedures that worked, he stuck to them as doctrine.
